System for preventing interference between power wires and communication wires



Oct. -1-1, 1932-.-

' A. HERZ SYSTEI FOR PREVENTING INTERFERENCE BETWEEN POWER WIRESAND'COXHUNICATION WIRES Filed Sept. 4, 1931 3 Sheets-Sheet 1 I my;

Oct. 11, 1932 V v A. HERZ 1,881,574

, SYSTEM FOR PREVENTING INTERFERENCE BETWEEN rowan WIRES ANDCOMMUNICATION WIRES Filed Sept. 4, 1931 3 Sheets-Sheet 2 0a. 11. 1932; vA, HE 1,881,574

'SYSTBI FOR PREVENTING INTERFERENCE BETWEEN POWER WIRES ANDCOMMUNICATION WIRES Filed Sept. 4, 1931 3 Sh'OtS-Sh66 t 5 Patented Oct.11-,- .1932

UNITED STATES PATENT-OFFICE ALFRED HERZ, OF CHICAGO, ILLINOIS SYSTEMFORQPREVENTING INTERFERENCE BETWEEN POWER WIRES AND COMMUNICATION WIRESApplication filed September 4, 1931. Serial No. 561,170:

My invention relates .to system and method of preventing interferencebetween power conducting Wires and communication wires and the like. Thepresent application 1s an 5 improvement upon my prior Patent No.1,782,875, of November 25, 1Q30, and also upon my copending application,Ser. No. 382,025, 'of July 29, 1929.

When a modern power transmission line is built some consideration isgiven to'adjacent communication circuits already in existence bycoordinatin the configuration and arrangement of the power line wires sothat a minimum inductive influence is felt by the communication circuitswhile normal operating conditions exist on the power system. Thisminimizing of inductive influence is brought about by transposing thepower wires at certain pre-determined points so that the influenceexerted by the individual power wires has substantially equal effect onthe wires of given communication circuits. Assuming the separation ofthe two lines to be strictly equal throughout the exposure, each of thepower'line wires is caused to occupy a given position on the pole ortower line for one third of the total length of exposure. Naturally ifthe exposure is not strictly a physical parallel, as, indicated above,but so there is some variation in separation between the two systems,this can be compensated for, at least to some extent, by varying thelength of the sides of the transposition barrel, this latter-being therecognized term which covers the equivalent of the three transpositions,in the ease .of a three phase power line, necessary to bring a givenWire back to the nominal location originally occupied by it. Thus,outside of slight unbalances due to variation in fl 40 height, sag,etc., a theoretical cancellation of the influence is obtained. Theslight remnant is further reduced in the case of metallic telephone,circuits by a frequent transposition of the pairs constituting thelatter system.

The above, as indicated before, relates to normal operating conditionsof the power system. In case of abnormals, and most especially in thecase of a short circuit to ground, the three phase field is so badlydistorted that it usually essentially becomes a single phase field, thewire or wires in trouble constituting one side of a loop and the returnpath being under the surface of the earth, the plane of the return pathoften ex- 5; tending one or more thousands of feet under ground. Thenthe aforementioned coordination, i. e., transpositions, do not to anymaterial extent mitigate influences felt by the communication wires. Itis under this latter condition that the screen Wires are effective,since a counterflux' is generated by these which to a great extentcancels the single phase flux liberated by the fault current and itsreturn through the earth.

Returning to the normal operating condition of the power system, thebenefits derived from transpositions of the power conductors are basedentirely on the principles of an uninfluenced three phase field spaced120 electrical degrees apart andof equal magnitude. If a wire such as ascreen wire is placed comparatively physically close to these powerwires and'if this screen Wire in turn is grounded at more places thanone, which is essential in order to make it perform as a screen wire, acurrent will be induced in it the same as a current is induced in theshort circuited secondary of a transformer unless the screen wire islocated in such a position that it is equally influenced b the field ofall three of the power wires. TlllS condition is practically impossiblewith a line configuration which works out best for structural andeconomical reasons. Therefore a single wire can only occupy a positionwhere the influence is unequal and therefore, as mentioned before, acurrent will be caused to ow. I have conceived the possibility that thiscontradictory condition, that is, where a screen wire offers bothmitigating and harmful effect, can be alleviated if another harmfuleffect of equal magnitude but of opposite phase is caused to make itsappearance. I propose, in brief, to employ two screen wires so arrangedas to oppose the harmful influence of each other while gaining thebeneficial effects of both.

e individual wires of the pair are so locatedthat the small voltageinduced, when no the line is operating normally, in one screen wire, iscompensated for by anequal voltage but in opposite phase in the otherscreen wire, these two being either transposed, and thus having thetotal effect nullified, or else not transposed andallowing thecirculating current to flow between these two screen wires via thecircuits between the wires at these grounding points. Thus, although thecirculating current does flow it has no effect on a neighboringcommunication wire as long as the circulating current stays in the smallloop consisting of these two screen wires. If, however, these two screenwires are not balanced by being in opposite phase, the circulatingcurrent will flow through the ground connection and through the earth,thus creating a large loop which does affect neighboring communicationwires.

In accordance with the present invention I provide, also, a particulardisposition of the shielding conductors with respect to the powerconductors, so as to gain the-maximum neutralizing effect. That is tosay, with the two conductors of the shielding system of my presentinvention, it is possible to dispose the shielding system in a moreadvantageous manner than where a single conductor is employed for thatpurpose. Also it is possible, according to my present invention, toemploy a single pair of shielding conductors constituting theanti-induction system for two adjacent power lines upon the sametransmission tower or other common support, all without appreciablechange from the usual location of the power conductors.

Now, in order to acquaint those skilled in the artwith the manner ofconstructing and operating the system "embodying my invention andpracticing my method, I shall describe, in conjunction with theaccompanying drawings, a specific embodiment of the invention.

. In these drawings:

Figure 1 shows the shielding conductors as applied to a high voltagepower line;

Figure 2 illustrates a shielding conductor applied to a communicationsystem which extends parallel to the power system shown in Figure 1; thecommunication line of Figure 2 parallels the power line of Figure 1, asindicated in Figures3 and 4;

Figure 3 is a diagrammatic circuit representation showing acommunication line which parallels a power line, and also the shieldingconductors provided in-connection with these lines, the grounding pointsthereof, and the manner of transposition of certain shield conductorsrelative to the power conductors;

Figure 4 represents another diagrammatic circuit in which groundedshield conductors are shown to be arranged in sections and transposedwith regard to the conductors of the power line; and

ssn574 Figure 5 shows a cross sectional view of a;

Referring now to Figure 1, this figure shows, somewhat,diagrammatically, one -tower of a high tension transmission systemwherein the conductors are disposed in substantially thearrangementshown in Figure 5. Mounted on the tower 1 are the cross-arms2, 3 and 1, all of the usual trussed or any preferred construction. Thehigh voltage power conductors 5, 6, 7, and 8, 9, 10 of two feeders aresuspended from the cross-arms in the usual or any preferred manner bymeans of high voltage suspension insulators 11, 12, 13 and 14, 15, 16,respectively. An electrostatic shield conductor 17 extends parallel tothe power wires. This conductor is optional, so far as my presentclaimed invention is concerned. .In Figure 5 I show two such conductors,17A and 17B.

This conductor 17 may be grounded at each of the supporting towers by adirect connection. It is provided for maintaining a ground potentialabove the power conductors. The grounding of this conductor 17, assumingthe same to be continuous, would be in effect the same as anelectrostatic shielding conductor, in that it is grounded by lowresistance ground connections at numerous points along its length.Preferably I place an insulator 110 or resistance such as shown at 111,which may be of carborundum, thyrite or the like, in each section of thegrounded conductor 17 between adjacent ground points and thereby preventor limit the longitudinal flow of current but provide low resistancepaths to ground. This eliminates or limits the objectionable effect uponthe communication line of induced current flowing in this conductor butpreserves the function of con ductor 17 as an electrostatic shield. Themanner in which I separate this conductor in sections by means ofinterposing insulators or resistances at certain points is indicated inFigure 3.

The sections into which the electrostatic shield wire is dividedare tobe either entirely insulated from each other or else connected with eachother through such a high resistance that the current caused to flow byinduction is reduced so that its effect upon neighboring communicationor signal wires is negligible.

Referring again to Figure 1, it will-be seen that I have provided twoanti-induction shielding conductors 18 and 19 in proximity to bothfeeders of the power line. The communication system to be protected bythese shield wires is shown somewhat diagrammatically and on an enlargedscale in Fi ure 2.

In Figure 5 the relation between the power line and the communicationline is indicated substantially to scale. Thepower linecomprises the twofeeders, 5, 6, 7, supported atila'rly, the vertical sag of the phaseconductor B'is indicated at 68 and similarly the vertical sag of theconductor"? is indicated at 78.

In addition to this, the conductor in each span, when thus permitted tosag verticall may swing sidewise through an angle indicated inconjunction with the insulator string 13 and conductor 7. While theswing is indicated only to the right of the neutral or vertical positionit is understood that the swing may be as great to the left, or in aclockwise direction. Interference with the power does not occur becausethe sag occurs between towers and the extent of angular motion indicatedwill bring the conductor 7 at the tower only so close as the length oftheinsulator string 13, as a radius, permits.

In the layout shown in Figure 5 the angle A is 45.

The dimension B between the nearest communication conductor and theswing of the nearest power conductor 7 is approximately 12 6". The othergeneral dimensions have been indicated on Figure 5-to show the generalproportions of a specific embodiment.

It will be observed that the three phase conductors of each feeder aredisposed at the corners of a flat triangle on each side of the tower 1.The two conductors 18-19 which form the sides ofv an anti-induction loopare so disposed relative to the power conductors that they havesubstantially equal effect upon the two feeders, and also eachanti-induction conductor 18 or 19 has substantially the same effect uponeach line that the other has.

These two conductors 18 and 19 form a vertical loop which may betransposed as shown in Figures 3 and 4 or which need not be transposedunder certain conditions, forming in effect a vertical ribbon conductorextending through a plane which is substantially equally effective uponboth feeders. If an actual metallic ribbon were so disposed, only theupper and lower edges would, in fact, have much effect and therefore twospaced conductors such as 18 and 19 are substantially the equivalent ofa vertical ribbon of metal. The two conductors 18 and 19 area as 113,which may be employed under certain circumstances to assist in limitingcirculating currents.

I prefer to prevent circulating current occurring through ground and thetwo antiinduction shield wires such as 18 and 19, by transposing thesaid anti-induction shield wires between grounding points with very lowresistance in the ground connections.

The residual field which might affect the two anti-induction shieldingwires 18 and 19 within the length of power line between transpositionswould induce voltages which would tend to set up current fiow in oneconductor such as 18 in one direction, and in the other conductor suchas 19, in the op posite direction, with the result that a circulatingcurrent would tend to flow. However, if within the length betweentranspositions of the power wire the two conductors 18 and 19 which areconnected together at the transposition points of the power wire byground connections are themselves providedwith a transpositionconnection, the two voltages oppose each other and substantiallyeliminate circulating current but at the same time provide a highlyconductive path for ground return current in case of a single phase toground fault.

Thus maximum usefulness of both conductors in parallel for ground returncurrent, and the two conductors in opposition to each other foreliminating circulating current due to residual field, under normalconditions, is secured. Y

The communication line shown in Figure 2 parallels the power systemshown in Fi ure 1 for a greater or lesser distance, depen ing upon theinstallation. The communication line may comprise pairs of conductorssuch as 20, 21, and 22, 23, for full metallic circuits. Theseconductorsare shown to be supported upon insulators 23, 25, 26 and 27,respectively, which may be mounted on the cross-arm 28. .Several suchcross-arms carrying insulators and communication wires supported therebymay be mounted on the customary pole structure indicateddiagrammatically at 29.

An insulator 30 is mounted on the pole 29 for supporting the shieldingor screen wire 31. This shielding wire is a conductor of low resistancewhich extends parallel to the communication conductors and is groundedcarefully at a number of points along its length, i. e., at the poles,for example, in a manner as is indicated at 32.

If it is desired to achieve only an electromagnetic shielding effect,this conductor 31 may be mounted on any convenient insulator, preferablycentrally of the insulators. which support the communication wires. Itsparticular location relative to the service wires does not seem tomatter materially. It will have a mitigating efiect upon the elech'omlgnetic fields. However, when the shield ill ' determined bylocalconditions.

wire. 31 is placed above the service wires, for example in the manner inwhich it is shown in Figure 2, its eflect will be to shield thecommunication system electrostatically as well as electromagnetically.It will re-- tain its mitigating eflect upon the electromagnetic fields,and it will at the same time render an a preciable efiect in screeningthe communication line from electrostatic interference.

Reference may now be had-to Figure 3 which shows a power system, acommunication system extending in parallel thereto, and the shieldconductors for eliminating the detrimental efi'ects of the first systemupon the second system, as provided in accordance with my presentinvention. I

The conductors 83, 34, 35 of the power line are transposed at a numberof points designated by the numerals. 36 to 42, inclusive. The distancebetween transposition points is The three conductors are in effecttwisted about each other for a complete turn and then twisted back againa complete turn, etc. The length of power line between which theconductors are thus twisted for a complete turn is called a barrel. Thelength between the points 43 and 43 as shown in Figure 3 represents sucha barrel, or, rather to say, these points are the uncture points betweenadjacent barrels of the power line. The transposition is omitted atthese points because they are, in effect, the equivalent oftransposition points because of the reversal of twisting. In each Ibarrel the three power conductors occupy the successive positions forsubstantially equal lengths, hence, other factors being equal, theinductive effect upon adjacent communication lines, insofar as the powercycle hum is concerned, and if spaced a substantial distance from eachother, is substantially neutralized. The barrels may be of differentlength as conditions require.

Two conductors of a communication system are indicated in Figure 3 bythe numerals 44 and 4 5. A shielding conductor 46 is shown adjacent thecommunication line. This conductor may be grounded at each of thetransposition points of the power line and at points which are theelectrical equivalent of the transposition points, such as the nodepoints 43 and 4 3.- These grounding connections are indicated at 47 to55, inclusive. The shielding wire 46 may correspond to the shieldingwire 31 shown in Figure 2. -When disposed over the'communication line itwill mitigate not only the electromagnetic forces acting upon thecommunication line, but it will also act as an electrostatic shield, aspreviously explained.

A low resistance path in each loop of this shielding wire is highlydesirable and if good ground connections are not available it isadvisable to resort to a metallic return wire connected to the foot ofthe tape 47 to 55, which Ihave shown in Fig. 3.

In order to maintain a ground potential at or above the power line, Iemploy one or more sectionalized shielding wires such as 17 in Fig. lor17A17B in Fig. 5, the different sections being indicated at 56 to 68,inclusive. The various sections may be conductively sectionalized bymeans of insulators 110 or resistances 111 at points between the towerssupporting the power line. Each section is connected by a low resistanceconnection to ground as shown. a

, This sectionalized conductor performs the function of an electrostaticshield. Due to the insulators 110 placed between the sections the flowof current is prevented between adjacent grounding points, andobjectionable effects of current flow in this conductor are avoidedwhile the electrostatic shielding function is fully preserved. Insteadof a sectionalized conductor as described, individual sections ofconductors may be provided if desired. It is, in some cases, notnecessary to employ insulators 110, as resistances 111, which limit thelongitudinal flow of current along the electrostatic conductor, aresufficient. The object in each case is to provide free paths for thesections to ground, but to limit or even prevent theflow of inducedcurrent longitudinally of the electrostatic shield wire. WVith eitherinsulators 110 or resistances 111, impulse voltages may travel toadjacent sections and thence to ground.

The two anti-induction shielding wires such as 1819 may be conductivelycontinuous conductors such as indicated in Figure 3 by the numerals 69and 70. The relative location of these conductors with respect to thepower conductors is apparent from Figures 1 and 5 and also from thediagram Figure 3. The manner in which these shielding conductors may beplaced on the supporting towers of the power line may be varied. Theymaybe insulated from the tower and grounded by separate ground taps orthey may rest directly upon the metallic parts of the tower and begrounded therethrough.

It will be first assumed for the sake of explanation that these wiresare two separate conductors mounted on the towers of a power line, andthat they are grounded at various points, for example, substantially atthe points of transposition ofthe power line. It is further assumed thatthese conductors are continuous and that they are disposed substantially in parallel to each other and to the power line, includingsubstantially the same sag, without any transposition relative to oneanother. If this condition is assumed to be the case .it will beunderstood that voltage induced in either one of these wires will shieldwires and a loop formed by them is concerned, and this force will set upcirculating currents in the shield wires. The effect of the circulatingcurrents preferably should be neutralized in such a case where twoshieldin" conductors are em *cd. If

a: l l

the resultant voltage of the two induced volages is permitted .to makethe relatively 'large loop formed by flowing to and through ground, thedisturbance upon the communication wire might be worse than if they wereabsent. This may be prevented by inserting enough resistance in theground taps to limit the current flow or the two wires may be of lowresistance. They are of a conductivity substantially equal to the phaseconductors. The conductors are grounded at or near the points oftransposition of the power line as shown in the diagram, whereby thephase of the E. M. F. on the shielding conductors is more closelyadapted to the phase of the residual inducti'ng magnetomotive force ofthe particular section. The cross-connecting grounding connections forthe shielding wires are indicated by reference numerals 72 to 78,inclusive. The shielding wires are twisted or transposed approximatelymidway between the grounding points, or at such-a point as will securethe desired opposition of the induced electromotive forces. The voltageinduced in each half of a loop of these shielding conductors will thusbe opposed and thereby cancelled by the voltage in opposition in theother half. Thus the anti-induction shield wires do not normally carrycurrent. This means that they do not tend to cause loss from themaintenance therein of a current flow, the power for which would have tobe supplied by the transmission line. However, in case of ab-- normalconditions such as a fault to ground, the two conductors 6970 formparallel paths for the return current.

In Figure 4 I have shown another embodiment of realizing the preventionof circulating current effects in the loops of the two shieldinconductors employed in conjunction wit a power line.

Numerals 79 and 80 in Figure 4 designate a communication line. A.shielding conductor 81, grounded at points 82 to 87, inclusive, may beprovided for protecting this communication line against electromagneticeffects ofthe adjacent power line. If this conductor 81 is placed overor on approximately the same line as the communication lines, aspreviously explained, it will also act cross-connecting I as anelectrostatic shield for the communication wires. The grounding pointsof this shield wire may substantially correspond to the transpositionpoints of the power wires and to node points thereof, respectively, asillustrated.

The power line shown in Figure 4 comprises the conductors 89, and 91.These power conductors may be suitably transposed in accordance with thelocal conditions as previously outlined. One barrel of the power line isformed between the points 92 and 93.

I employ sectionalized or conductively discontinuous shield conductorsin this embodiment. These shield conductors are indicated at 92'93',9495, 9697 and 9899. They are cross-connected and grounded by means ofthe connections 100101, 102-103, l 04.-105 and 106107, and aretransposed intermediate of the grounded cross-connections as shown, inorder to neutralize the efl'ect of circulating currents which will beinduced in the loops of the shielding wires. It is understood, ofcourse, that the cross-connections and the grounding wires may beseparate in this embodiment, as well as in the embodiment previouslydiscussed with reference to Figure 3.

The function of the above described arrangement shown in Figure 4 is, inefi'ect, substantially the same as the function of the previouslyexplained arrangement represented diagrammatically in Figure 3. Voltagewill be induced in each half of the loops of the grounded shieldingwires and the effect of the voltage induced in one half will becancelled or neutralized by the effect of the voltage induced in theother half due to the transposition of the shielding wires.

The terms employed in the foregoing specification and also in theappended claims are intended to cover broadly the subject to which theyrefer. 'For example, as has been mentioned elsewhere in this secification, the

terms communication and signalling are 7" used to include telegraph,telephone, and all other systems in which equipment is actuated overlines by relatively weak currents either over full metallic circuits orby the use of ground return. Systems of this or of broadly similarcharacter, including'systems operating phantom or superimposed circuitsare understood to be also covered by these terms.

shown and discussed. What I consider new and distinguishing over priorinventions is particularly defined in the following claims:

I claim as my invention: 1. In an electric system wherein a powertransmission system and a communication system parallel one another,means for preventing the induction of excessive'voltages in thecommunication lines due to curre t flowing in the power line, said meanscomprising shielding conductors disposed substantially parallel to andin the vicinity of the power line, said shielding conductors beingintermittently grounded and transposed intermediate of the groundingpoints thereof. 2. In an electric system wherein a power transmissionline and a communication line are disposed substantially in parallel toone another, a plurality of shielding conductors for preventing theinduction of excessive voltages in said communication line, means forgroundin saidshielding conductors at predetermined points, saidshielding conductors being transposed intermediate of said groundingpoints for neutralizing the effect of currents circulating therethrough.

3. In an electric system wherein a power transmission line and a'communication line are disposed substantially in parallel to oneanother, a plurality of shielding conductors extending in the vicinityof said power line and substantially parallel thereto for reducing theeffect of magnetic fields of said power line upon said communicationline, means for cross-connecting and for grounding said shieldingconductors at predetermined points, and means for neutralizing theelectromagnetic effect of currents induced in said shielding conductorsshielding conductors and circulating therethroug N 4. In an electricsystem wherein a power transmission line and a communication line aredisposed substantially in parallel to one another, the condutitors ofsaid power transmission line being transposed at predetermined points,means for reducing the effects of electromagnetic and electrostaticforces of said power transmission line relative to said communicationline said means including a plurality of shielding conductors disposedin the vicinity of said power transmission line and substantiallyarallel thereto, said eing transposed at predetermined points, thepoints of transposition of said shielding conductors being intermediateof the points of transposition of said power transmission conductors,and means for'connecting said shielding conductors intermediate of thepoints of transposition thereof. 7 y

5. In an electric system wherein a power transmission line and acommunication line are disposed substantially in parallel to oneanother, the conductors of said power line being transposed atpredetermined points, means for reducing the effects of electromagneticand electrostatic forces of said power line relative to saidcommunication line, said means including a plurality of shieldingconductors disposed in the vicinity of said power line and substantiallyparallel thereto, said shielding conductors being transposed atpredetermined points, the points of trans position of said shieldingconductors being intermediate the points of transposition of said powerconductors, means for cross-connecting said shielding conductorsintermediate of the points of transposition thereof, and means forgrounding the points of crossconnection ofsaidshielding conductors, thegrounding points of said shielding conductors being disposedsubstantiall coincident with the transposition points 0 said powerconductors.

6. In combination witha power transmission line, means for reducing theinductive a' effect of said line relative to a communication linedisposed substantially parallel thereto, said means including aplurality of shielding conductors transposed at a plurality ofpredetermined oints', and means for interconnecting and or groundingsaid shielding conductors lntermediate of said transposition pointsthereof.

7 In an electrlcsystem comprising a power transmission line and acommunication line disposed substantially in parallel to said powerline, the conductors of said power line being transposed atpredetermlned po1nts, means for shielding said communication lineagainst the efiect of electromagnetic and electrostatic fields createdby the currents flowing in the conductors of said power l1ne, said meanscomprising a shielding conductor disposed over said communication 11ne,grounding connections for said conductor substantially coincident withthe points of transposition of said power line, two shielding conductorsdisposed substantially parallel with said power line, said shieldingconductors being' -transposed at predetermined points intermediate ofthe points of transposition of said power line, means forcrossconnecting said shielding conductors intermediate of the points oftransposition thereof, means for grounding said shielding conductorssubstantiallv coincident with the. transpositions of said powerconductors an electrically discontinuous shielding con uctor disposedover said powerconductors, and ground connections for the sections ofsaid discontinuous shielding conductor for maintaining a groundpotential over said power conductors. I

8. In combination with an overhead power line, a conductor disposedabove and parallel to said line, said conductor comprising a number ofsections insulated from one another and connected mechanically end toend, each section being directly grounded to maintain each sectionnormally at ground potential, a pair of conductively continuousshielding conductors disposed substantially parallel -to said line, saidshielding conductors being transposed at predetermined points, means forcross-connecting said shielding conductors intermediate of said pointsof transposition thereof, and means for grounding said points ofcross-connection of said shielding conductors.

9. A system of the class described, com? prising an alternating currenttransmission line having conductors, said conductors being transposed, acommunication line having conductors influenced electromagnetically andelectrostatically by said transmission line, a plurality of shieldingwires adjacent said power conductors, said shieldin wires beingtransposed, and a shielding wlre disposed above said communication line,said shielding wires having ground connections atintervals correspondingsubstantially to the points of transposition of said transmission me. I

10. In combination with a power line and an adjacent communication line,an electrostatic shield wire comprising a plurality of sections, saidsections being provided with individual low resistance groundconnections and the sections being joined by connections of such highresistance as to reduce the current flow caused by voltage induced bythe normal flow of power on the power line to a negligible value, saidresistance providing a relatively free path for impulse voltages.

In witness whereof, I hereunto subscribe I my name this 2nd day ofSeptember, 1931.

ALFRED

